Synthetic pentasaccharides

• pentasaccharides are synthetic drugs that accelerate the interaction between factor Xa and antithrombin
  • induce a conformational change in antithrombin
    • unlike unfractionated and low-molecular-weight heparins, pentasaccharides do not affect the interaction of antithrombin with thrombin and thus selectively inhibit factor Xa activity
    • fondaparinux is a pentasaccharide with a half-life of approximately 17 hours
    • idraparinux is a long-acting pentassacharide, with a half-life of about 80 hours

A table comparing the properties of pentasaccarides to low molecular weight heparin is presented below:

* monitoring is required in patients with a creatinin clearance of less than 30 ml/min by anti-Xa concentrations.

** low-molecular-weight heparins are less likely to induce thrombocytopenia than unfractionated heparin, because these interact less with platelets and platelet factor 4 (an essential feature of heparin-induced thrombocytopenia). Pentasaccharides do not interact with platelet factor 4 and platelets and thus are very unlikely to induce thrombocytopaenia (1).

Trial evidence suggest that fondaparinux is as good as, and possibly better than, low molecular-weight heparin for the prophylaxis of post-operative deep venous thrombosis in patients undergoing hip replacement (2).

Reference:

• (1) Savi P et al. Effect of fondaparinux on platelet activation in the presence of heparin-dependent antibodies: a blinded comparative multicenter study with unfractionated heparin. Blood 2005;105 (1): 139-144.
• (2) BMJ. 2006 Jan 28;332(7535):215-9.